Manufacture of stabilized concentrated hydrazine compositions



1 States 1 atent O John F. Haller, Niagara Falls, N. Y., Mathieson Chemical Corporation, Virginia No Drawing.

assignor to Olin a corporation of Application December 24, 1954 Serial No. 477,598

' 18 Claims. 01.23-190 This invention relates to the stabilization of concentrated hydrazine, providing, more particularly, a process for the stabilization of hydrazine containing 95 percent or more of anhydrous hydrazine and a stabilized concen trated hydrazine product.

This application is a continuation-in-part of my copending application Serial No. 297,761, filed July 8, 1952, and now abandoned. Hydrazine has been known for a long time. It has usualy been available only in the form of its salts and as hydrazine hydrate, a constant boiling composition comprising approximately 2 parts by weight of hydrazine to 1 part by weight of water. More recently, however, substantially anhydrous hydrazine comprising at least 95 percent N H by weight has becomean article of commerce. Hydrazine hydrate is comparatively stable in storage and use compared to the 95 percent hydrazine. The latter can decompose in storage, particularly in the presence of certain metals or metal compounds. Stabilization of the concentrated hydrazine with respect to decomposition is important in order to avoid extensive losses and hazard in manufacture, in storage and in use.

I have discovered that the stability of concentrated hydrazine, particularly as prepared by the Raschig process,

is associated with a property most simply explained as its potential acidity which can be neutralized, treating the hydrazine as the dissociating medium or solvent, by the addition of basic substances. I have also found that the corrosiveness of hydrazine to metals is associated with this same property. By further investigation, I have found that the potential acidity causing undesirable instability and corrosiveness can be satisfactorily neutralized and buttered by addition of a small amount of a metal oxide which is not reactive with hydrazine and which functions as a weak base. Suitable metal oxides for this purpose are aluminum oxide, zinc oxide and cadmium oxide. For example, the addition of a small amount of zinc oxide stabilizes concentrated hydrazine, buffering it so that the resulting product has markedly improved resistance to decomposition. Hydrazine solutions of a greater concentration than hydrazine hydrate up to substantially anhydrous 100 percent hydrazine can be stabilized by this means. Suitable proportions of the oxides can vary from about 0.2 to 5 percent by weight. Ordinarily about 1 percent of the oxide gives satisfactory results. Less than the lower limit recited may be insufficient and more than the upper limit does not appear to be necessary. The oxides used can be chemically pure or can be an ordinary commercial grade.

The oxide can be added to the hydrazine during manufacture to prevent its decomposition at any stage where the concentration is greater than that of hydrazine hydrate. It can be added to finished 95 percentby weight 2 hydrazine as it is loaded into drums or tank cars for storage or shipment. The insoluble excess oxide is easily removed by settling and decanting or by filtration, and the hydrazine product can be distilled prior to use if deemed necessary or desirable.

in a particularly advantageous modification of the present invention, the metal oxide such as cadmium oxide,

is used as stabilizing agent in fractionating columns in which hydrazine having a concentration greater than that of hydrazine hydrate is produced. Insteel equipment used in extractive distillation processes for the dehydration'of hydrazinehydrate to form substantially anhydrous hydrazine, serious decomposition difficulties are encountered. Introduction of cadmium oxide or other metal oxide into the fractionating column effectively avoids such decomposition and stabilizes the hydrazine.- The cadmium oxide, for example, can be introduced by any suitable means, for example, by saturating the by drazine hydrate feed with cadmium oxide. A particularly advantageous mode of introducing the cadmium oxide comprises preparing a slurry of cadmium oxide in water or hydrazine hydrate and pumping the slurry into the top of the tower before continuous operation begins. The slurry can also be introduced in the same way while operating. Using extractive distillation with aniline to dehydrate hydrazine hydrate, for example, as described in copending application Serial No. 361,185, filed June 12, 1952, now Patent Number 2,773,814, the cadmium oxide can be slurried with aniline, water or hydrazine hydrate and introduced into the top of the column. Aniline is circulated through the system from the reboiler to the top of the column for several hours at operating temperatures and the continuous operation is then started by feeding hydrazine hydrate to the column. The cadmium oxide becomes distributed on the trays and prevents hydrazine decomposition in the tower. In one such operation after such a cadmium oxide treatment, the column operated continuously for 21 days and then was shut down for other reasons.

EXAMPLES 1-6 position are shown in the following table:

Table Decomposition, Decomposi- Percent/day tion Rate Example Accelerator Added Ratio With No. ZnO/With- Without With out 2110 2110 ZnO None 0.0918 0. 0027 1/34 N1(0GOOHr)z.4HzO .0875 .0043 1/20 Fe(OH)(OGOCHs)z .235 .013 1/18 Al2(SOi):i.18HzO 116 0012 1/97 Cl7(SO4)3.5HzO .308 0027 1/114 Cu(0 COCHsMHzO 1.66 0006 1/277 In each of the six examples, grams of hydrazine was heated under reflux. When a metallic compound 1C Patented June 3, 1958 was added as an accelerator the concentration of metal was 20 parts per million. .In Example 1, 2 percent by weight of i to obtain an .accurately measurable sample varied from about 4.5 to 45 hours. fiuxing hydrazine was about1l3 C.

acetate.

EXAMPLE 7 ing the aniline overhead and condensing and recycling it to the aniline make-up line entering the tower. small amounts of cadmium oxide eventually appeared in the form of suspended particles in the reboiler liquid, normal operation was started by feeding hydrazine hydrate to the column.

.In this normal operation, the still was operated at about atmospheric pressure with a top temperature of about 100 C. and .had a bottom temperature of about recovered therefrom by distillation at a 4:1 reflux ratio in a hydrazine still having 7 Continuous normal operation days without interruption and was operating satisfactorily without hydrazine decompo sition when the operation was shut down for other reasons. The particular amount of cadmium oxide employed in this run of 21 days was not critical, inasmuch The temperature of the reas' satisfactory results pounds or .30 pounds of cadmium oxide instead of 10 pounds.

was produced.

In this example neutralization and stabilization of the hydrazine was effected in the azeotrope still by the introduction of cadmium oxide. Further treatment with cadmium oxide in the hydrazine hydrazine is uncertain or some time has elapsed after treatment according to theprocess of this invention.

EXAMPLE 8 In parallel tests, a sample of 96.8 percent hydrazine alone and the same hydrazine to which reflux, collecting the evolved gases. Decomposition of the untreated hydrazine occurred at the rate of 0.142 percent per 24-hour day and-at the rate of 0.069 percent per day for the sample containing alumina. Y

I claim:

1. In hydrazine compositions having a molar hydraz1ne-water oxide ,in amount suificient to substantially inhibit the decomposition of hydrazine.

2. A method according to claim 1 in which said metal oxide is aluminum oxide.

3. A method according to claim 1 in which said metal oxide is zinc oxide.

4. A method according ,to claim 1 in which said metal oxide is cadmium oxide.

5. In a method for the manufacture of concentrated hydrazine tilling aqueous hydrazine, the step of incorporating into the hydrazine being fractionally distilled a metal oxide selected from :the group consisting of aluminum oxide,

undergoing fractionation.

6. A method according to claim 5 in oxide is aluminum oxide.

7. A method according to claim 5 in which said metal oxide is zinc oxide.

which said metal 8. A method according to claim 5 in which said metal.

oxide is cadmium oxide.

9. The method of stabilizing concentrated hydrazine the decomposition of the hydrazine.

10. A method according to claim 9 in oxide is aluminum oxide.

11. A method according to claim 9 in which said metal oxide is zinc oxide.

12. A method according to claim 9 in which said metal oxide is cadmium oxide.

13. vA method accordingto claim 9 in which the amount of said metal oxide incorporated into the hydrazine is within the range from about 0.2 to 5 percent by weight, based upon the weight of the hydrazine.

which said metal 14. A stabilized concentrated hydrazine product which consists essentially of a-concentrated hydrazine composition'having'a molar hydrazine-water .ratio greater than that of hydrazine hydrate to which has been added a metal oxide selected from the group consisting of aluminum oxide, zinc oxide and cadmium oxide in amount sufficient to inhibit the decomposition of the hydrazine.

15. A product according to claim 14 in which said metal oxide is aluminum oxide.

16. A product according to oxide is zinc oxide.

17. A product according to claim 14 in which said metal oxide is cadmium oxide.

18. A product according to claim 14 in which the claim 14 in which said metal amount of said of the hydrazine.

metal oxide added is within the range fiom References Cited in the file of this patent UNITED STATES PATENTS Marshall J an. Haller Apr. Haller Apr. Mantell et a1 Dec 

1. IN A METHOD FOR THE MANUFACTURE OF CONCENTRATED HYDRAZNE COMPOSITIONS HAVING A MOLAR HYDRAZINE-WATER RATIO GREATER THAN THAT OF HYDRAZINE HYDRATE, THE STEP OF INCORPORATING INTO THE HYDRAZINE COMPOSITION A METAL OXIDE SELECTED FROM THE GROUP CONSISTING OF ALUMINUM OXIDE, ZINC OXIDE AND CADMIUM OXIDE IN AMOUNT SUFFICIENT TO SUBSTANTIALLY INHIBIT THE DECOMPOSITION OF HYDRAZINE. 